Improvement in navigators  protractors



NITED Tareas JOSEPH D. LEACH AND SEWALL LEAGH, 0F PENOBSCOT, MAINE.

IMPROVEMENT IN NAVIGATORS PROVTRACTORS.

Specification forming part of Letters Patent No. 178,535, dated June 13,1876; application filed March 6, 187'6.

To all whom it may concern Be it known that we, JOSEPH D. LEACH andSEWALL LEAOH, both of Penobscot, in the State of Maine, have invented aNavigators Protractor, ot' which the following is a specification Theobject of our invention is to furnish to mastermariners a certain,positive, and reliable-instrument, by the aid of which they may be ableto demonstrate upon their charts the eX- act course, by compass, to bepursued from the port of departure to the port of arrival, or thedirection, by compass, from the given position of the vessel to the portot' arrival, or the direction, by compass, of any given point on thechart from any other point thereon, without the use of parallel rules orthe instrument usually employed for such purpose;`

and the. invention consists in combining, with a circular cardsubdivided and marked inthe usual manner ofcompass-cards, with astraightedge or rule, by means of a holder or socket for thestraight-edge, such socket or holder being pivoted to the center of thecard, and so constructed and arranged as that the line of one edge ofthe rule shall pass directly through the pivotal center of the socketand cart.

In the accompanying drawings, Figure 1 is a top or plan view ot' ourprotractor complete. Fig. 2 is a vertical section taken transverse torule b. Fig. 3 is a vertical section taken in the axial line ot' rule b.Fig. 4 is a section similar to Fig. 2, but showing a modication of therule or straight-edge holder.

In the above drawings, a represents the card. b is the straight-edge orrule. c represents the socket or holder. d is the beveled edge of therule. eis the pivot-plate. j' is the central pivot. g and g are thelockingbolts.` h is an intermediate plate between the pivot-plate e andthe socket-plate c. i is an auiriliary lockingbolt, and j is acontactspring.

rIhe construction and operation ot' our invention will be readilyunderstood by an eX- amination of the drawings, with but a briefdescription.

The card c is to be subdivided to any desired degree of ininuteness,and, as shown in Figs. 2 and 3, the plate c is pivoted to a by pivot j',so as to admit a free rotation of the parts relatively to each other.rlhe tpent or socketed plate c is secured to plate e by means of thescrew-bolts g and g', which are countersunk in plate c, and passedthrough slots in plate c, as is shown in Fig. 2. The rule orstraightedge I) is diminished in thickness a part of its length by theamount ofthe thickness of card a and plate e, so that the under I sideof the thick part ofthe rule and the bottom of the card form acontinuous line, to insure a perfect contact with the chart to preventslipping. The thinner part of the rule passes through the passage insocket-plate e, sliding freely therein. The plate c is adjusted by meansot' screw-bolts g and g', so that the edge of the rule will be exactlyover the center ot' pivot f, and as the lines upon the card all radiatefrom such center, therefore the edge of the rule will coincide with suchline, when brought in position.

A coiled spring, j, (shown in Figs. 2 and 4,) or a bent spring, 7c,(shown by dotted lines in Fig. 1,) serves to hold the rule in positionrelatively to the pivotf. In Fig. 4 the bolt g serves to lock the plateh in proper position upon plate e, while bolt g locks both plates c andL to plate c. The bolt i serves to lock plate c to plate lL. v

The stops l may be formed as a part of plate h, and serve as a bearingfor the beveled edge ot' the rule. A hole through plate h directly overthe pivotj', as shown in Fig. 4, as also the slot in plate c, and thespace between stops L in plate h, admit the accurate adjustment of theedge ofthe rule to the center of pivot f.

The practical use of this instrument may be described as follows: rIhebeveled edge d of rule b being placed upon the two points whoselrelative directions it is desired to determine, the card a is thenrotated and 'adjusted to such position that either the cardinal pointsnorth and south or east and west on the card shall coincide with arespective corresponding line on the chart, when the line on the card,coinciding with the edge d of the rule, Would indicate the relativedirections ot' such places from each other.

It will be apparent that it rule b were rigidly secured tQ the holder cthe same result might bearrived at; but the double movement of thecard-to Wit, its rotation and end move# ment relatively to rule b-admitsa more rapid adjustment, for when the rule is placed upon the twoApoints7 as stated, then, by means of such double movement of the card,two of its cardinal points can always be brought'to cof incide with arespective line on the Chart.

We claim as our invention- A navigators protraetor, eonsistingof` thecard ce, subdivided and marked as a compass-card, the rotary holder c,and rule b, the holder o being so pivoted to the center of card a at fas that one edge of rule b shall biseet pivotf, and the rule and holderbeing so oon- Strueted and arranged as to allow a lineal adjustment ofthe holder and card relatively to the rule, as well as a rotaryadjustment ofthe card relatively thereto7 all being constructed andarranged to operate substantially in Inanner and for the purposesSpecified.

JOSEPH D. LEAGH. SEWALL LEAOH.` Witnesses:

. ALBERT E. VARNUM,

CALVIN DAVIS.

